Safety paper



Patented June 30, 1942 I TED era-res PATENT OFFICE Q 2.28:3;14'7 I :SAFETYIPAPER Burgess -W. ESmith, Rochester, :Y., assignor 'to The Todd Company, Inc., Rochester, iN. Y.,Ja corporationof New York 'Ndprawing. .Ariplicatiori'March-lZ, 1941,

. eri rNassapso :9 claims.

This invention relates to; safety paper and; it comprises a safety paperhavingiincorporated therein small amounts of theleuco form' of 1a triphenylmethane dye so that upo'n the application of .a potassium permanganate 'ink .eradicater, a colored triphenylmethane dyeissdeveloped; it further:comprisessafety paper containing such leuco triphen'ylmethane "dyes, together with a coloreforming compound which develops color upon the application of 'hypochlorite solutions thereto.

.Safety paper for :making bank checks, :drafts, bonds, or other documents is composed 1 of a paper base impregnated with chemicals which develop a conspicuous stain or color upon the application of-chemical ink'eradicators. :In one form such chemicals :are "applied to the paper .by printing so that the word void, for example, flashes up in color when chemical .ink'erad- .icators are applied. For a .long :time the art hasdesired to broaden the scope of vtheresponse of such papers to ink .er'adicators. The most are various chemicals which :respond to this particular ink eradlcatoriby developing a conspicuous stainor color. Butmost of the .colorforming substances :used in .a safety paper I are not entirely satisfactory when ink eradicat'ors of the permanganate type are employed. A dilute solutionof potassium permanganate may causethese substances to develop color but when the permanganate-solution is followedby a reducing agent, suchas bisulfite of soda, the color" is discharged.

7 common eradicafor isa solution of hypoc h lorite =0: soda-preceded or followed by a solution .of

*anorganic acid, such as tartaricor oxalic. There Consequently, the art has sought waysof preical impregnant should develop a conspicuous color upon the application of these eradicators. Ithas been-particularly difficult to find chem ical substances which can be used'as an indicator when potassium permanganate eradicators are employed'for obliterating writing on the paper. The color-forming substances must de- :velop .a conspicuous stain and the stain must be resistant to theaction of bisulfite solutions or other reducing agents. I Ihave now discovered a class of chemical substances which .solve the problem gofflfind-ing a Suitable color-forming material reactive with potassium permanganate. This-class of .chem-' ical substances can 'bebroadly defined as the leuco form of the .triphenylmethane vdyes. -.Most

of these 'leuco dyes are, colorless and develop color upon the application of oxidizing. agents, such as,potassiu'm permanganate. The .color thus formed is resistant "tobleaching by .the application of *sodium bisulfite. ,"Moreover. these .leuco .derivatives of triphenylmethane dyes .de- ;velop -.color upon .the application of sodium :hypochlorite solutions. .Many-ofthe=.colored .com pounds thus formed are not :bleached entirely or completely by the application of "additional quantities of 1 sodium hypochlorite. Where these colored-compounds are markedly bleached'bysodium hypochlorite -I overcome, the disadvantage by i also impregnating the paper with colorforming chemical substances which are suitable .for use with sodium 'hypochlorite ink eradicators.

,Benzidineand many of its derivatives for example, develop aconspicuousrstain upon .theapplication of a hypochlorite underacidconditions and this stain isresistant to any, attempt to re- -move it by the application' of more sodiumhypochlorite.

. Thus the present inventionembraces first the preparation of a safety :paper containing {the leuco derivative of a triphenylmethanedye and second a safety paper containing a" leuco derivativeof a triphenylmethane dye, rtogether with other color-forming chemicals which are responsive to hypochlorite solutions. r

Priorart patents have disclosed many -hypochlorite-responsive, color-forming compounds which can-be used. Benzidine itself-is entirely satisfactory and various substituted benzidines,

such :as the sulfate, 'have been described. \Instead'of'benzidine I can use a diphenol since it is also reactive with hypochlorite solutions {to formrelatively permanent stains. :Consequently, in the appended claims-Ihave referred to color-forming chemicals reactive with-sodium 'hypochlorite solutions for the purpose of genericallydescribing this class of compounds. This language embraces substances 'ilke benzidine, benzidinesulfate, diphenols, .benzothia zole, and 'benzidine derivatives having substituentslin the 3,3 'positions. The latter .benzidine derivatives are more specifically described and claimed in my co-pending application, Serial No. 358,523 filed September 26, 1940.

A large number of the leucoderivativesaof the .triphenylmethane dyes have been'used in the practice of my.-invention. Among them are:

.Leuco of-PatentBlue A, of Kalle, Color Index'No.

714, ShultzNo. 545, "m-hydroxy-dibenzylethyldiamino-triphenylmethane, condensation product of m -hydroxy-benzaldehyde .and benzylethylaniline, Leuco of chrom Violet paste Bayer, Color Index No. 718, Shultz No. 549, tetramethylaminop -hydroxytriphenylmethane-m-carboxyli acid, condensation of t'etramethyldiaminobenzhydrol i and salicylic acid, Leuco of Aco Green paste of, Bayer, Color Index 675, Shultz No. 510, formed by couplingsalicylic acid withdiazotized'tetramethyldiamino-m-aminotriphenylmethane; and" 7' the leuco of tetraethyl-4,4'-Diamino-1" Sulfdtriphenylmethane. One of themost satisfactorydyes is the leuco,of that made by condensing paradiethyl amino-benzaldehyde with these tri'phenylnr ethane dyes'tare condensation products'between an aromatic aldehyde andlan aromatic amine. They. allcontain the triplienylmethane-- -nu'cleus. The -leuco-;.forms of these dyes' are 'generally' -colorless materials. ,A. newer the leu'coderivatives of the' triphenylmethane dyes are not. highly resistant to oxidation'and may develop slight color in the presence of air or light; "This tendency to slight coloration is not objectionable if the paper is tinted .to.

match the color whichmight-develop. due to this mild formof oxidation. Uponthe application of strongoxidation agents, such asa solution of rmanganate thereof course; the'full coloration of the colored form of the dye appears -This tendency to mild oxidation can be overcome by special ways of coating andv impregnating the paperbase as I shall presently describe. 7

Itfwould serve no useful purpose for' me to del h benzyl metatoluidine sulfonic acid. Many of surface layer.

ing or coating the paperuin-the manner'stated the paper can 'be'printed withjwa'rningjindicia using inks containing the leuco dye and inks containing 'Fthe benzidine compound. Thus, for example, I canprint the paper with the word void" using an ink vehicle containing any one of the leuco forms 'of the'triphenylmethane dyes and then print the paperwith inks containing benzidine sulfate or other color-forming chemicals responsive to hypo- ;chlorites, {a

Wetting agents can be added to the impregnating solution containing the leuco dye stuff so that-the'leuco dye is caused to penetrate throughout the safety paper.

v 1% of any I of the well known wetting agents added to' aqueous 'suspens'ionsof the leuco derivative will materially aid in securing, thorough impregnation of the paper base with' this: chemical. This expedient prevents any mild oxidationoi the leuco, d3? to a faintly tinted color since the dyeis idepositedlwithin the fiber structurepf thepap nd not asa s'imple,

Although I havemie fspe ficany e s'cri bedincarpal-sung both the leuco"dyesa ndthe'hypochloriteresponsive agents in the paper I do'not wish tobe limited toeusling 'bothfof thesecon- Ystituents. Thebenzidin'eor other chemical used scribe the leuco derivatives of. all the triphenyl- -metha,ne dyes which can be usedinthe practice I benzaldehyde is particularly efficient, I do-not wish .to be-limited thereto. However, I have discovered thatthe presence ofsulfonic acid groups in the triphenylmethane dye tends to stabilize the leucoform of the dye against anyminor oxidation phenomena whichmigh't occur in paper impregnat'ed therewith.

for ensuring lhypochlorite response 'canbe o'mitted. 'Theseleucofdyes in manycases giyea satisfactoryresponse to hypochlorites, and I 'am the first to have discovered their utility as indicators when permanganate bi'sulfitej eradicators' {are d... I w

' ,In general,

"in thisart. The application of amines or phenols claim is:

I known. Th

responsive to hypochlorite ink er adicators is well I leuco dyes herein described are'applied inthesame'way.

liavingthus described rn'y'inventi'on, what I l. A safety paper containing a leuco derivative ofa triphenylmethane dye.

2. A safety 'pap"r"containi'ng a leuco-derivative of a triphenylmethanedye"containingfsulfonlc The amount ofthe leuco dye and the color I forming substance responsive to .hypochlorites incorporated in the 'paper can'be varied over wide limits. A relatively small amount ofthese colorforming substances will develop conspicuousv stainsupon the application of ink eradicators.

As' littleas one-tenth of, one percent based on the w'eight of the paper is enough. Theleuco dye can be introduced in the beater as the 'mill,-or in a subsequent operation as they pulp is formed-into paper; or by any-suitable method of impregnating or coating. For example', a 1% solution or. suspensionof the leuco dye in the size applied to the paper can be used for impregnating the paper in the usual way. When the paper. is dried the application of permanga- "-nate ink eradicators thereto develops a permanent, conspicuous stain which is not discharged by'sodiumbisulfite. To paper which: has been sized or impregnated with .a solution or suspension' of the leuco dye stuff I can then apply a surface coating of benzidinesulfate. dispersed in a 3% solution of cellulose acetate in dimethyl phthalate or other suitable vehicle. claim to any particular vehicle for, the application I lay no of the benzidine sulfate. Instead of impregnatamino benzaldehyde.

acid groups, 3.. A safety paper containing the leucodr'ivative of the condensation product of ethyl benzylmetatoluidine sulfonic acid. and para :diethyl 4. Safety paperco'ntaininga leuco derivative of a triphenylmethane dye and'a color-forming chemical responsive 'tothe' action of'hypochlo'rite f 5. A safety'paper containing a leucoderivative solutions to form a e i.

of a triphenylmethane dye containing sulfonic acid groups 'and 'a'color-forming cheriiicalfre- ,sponsive to hypochloritesolutions to'form a'color.

' "6. Sa'fetypaper containing aleiico derivative of the condensation-product'of ethyl benzylmeta- 'jtoluidine sulfonic acid \and paradiethylamino befnzaldehyde and a color-forming chemicalreactive with hypochlorites to form a color. I

. contains a diphenyl linkage.

7. A safetypaper asj'in claim 4 wherein the hypochlorite-responsive, color-forming compound "8. The safety paper incla imj5' whereih*the hypochlorite-responsi've,' color forining com- I pound contains a diphenyl link'agei f 9.1Th safety paper as in"clairn6'wherein the hyp ponsiye, color-forming compound contains adiphenyl linka BURGESS w. SMITH.

however, the application or the color.-.fo1 ming compounds herein di's c lose'd*"to ithe paper base is no difierent'fronrthathitherto used- 

